In many computer graphics systems in use today, individual picture elements, i.e., pixels, of a graphical image are stored in a particular format. For example, single-band greyscale pixels are commonly stored as unsigned eight-bit integers, and 4-band color pixels are commonly stored as four contiguous unsigned eight-bit integers. Graphical images, which are generated using data representing a model and a computer process such as a three-dimensional modeling system, frequently involve complex numerical calculations. It is common for a graphical image to be rendered while pixels of the graphical image are represented in a format which provides greater precision that the particular format in which displayed pixels are stored. For example, in a computer graphics system in which each band of a displayed pixel is stored as an eight-bit unsigned integer, each band of a pixel is frequently stored as a sixteen-bit unsigned integer during processing and is converted to an eight-bit unsigned integer substantially immediately prior to display of the pixel. Such format conversion of each band of a pixel is generally referred to as recasting the pixel.
Recasting conventionally requires (i) loading from the memory of a computer a single pixel or a single band of a pixel at a time, (ii) converting the pixel or the band of the pixel to a display format, and (iii) storing the converted pixel of band of a pixel. Graphical images commonly have approximately one thousand rows and approximately one thousand columns of pixels, i.e., approximately one million pixels, and color graphical images typically include four bands per pixel. Therefore, recasting by such conventional techniques typically involves approximately four million load operations and approximately four million store operations. In addition, the recasting of a pixel or a band of a pixel typically requires at least one computer instruction per pixel or per band of each pixel. Therefore, approximately another four million computer instructions are required to recasting each band of each pixel of a typical graphical image.
Processing of graphical images typically requires substantial processing resources. Requiring substantial processing resources to recast the pixels of a graphical image into a display format only adds to the processing resources required to render and display a graphical image. Because of the substantial computer system resources required for such graphical image recasting, a need persists in the industry for ever increasing efficiency in recasting of pixels or bands of pixels of graphical images from a high-precision processing format to a space-efficient display format.